Conventionally, as acoustic signal encoding apparatuses, apparatuses that generate encoded acoustic data by transforming acoustic signals of a plurality of input channels into frequency domains and encoding frequency domain signals obtained through the transforming have been generally used. Accordingly, acoustic signal decoding apparatuses that decode the encoded acoustic data, thereby transforming frequency domain signals into time domain signals and outputting the signals as output acoustic signals, have become widespread.
Many of such acoustic signal decoding apparatuses have a function of outputting output acoustic signals corresponding to the number of output channels smaller than the number of input channels on the basis of a weighting coefficient for reducing the number of output channels of the output acoustic signals to under the number of input channels. For example, there has been suggested an encoded audio decoding apparatus that outputs decoded audio corresponding to the number of output channels by performing weighted addition using the weighting coefficient before transforming frequency domain signals of individual input channels into time domain signals (see, for example, PTL 1).
In this encoded audio decoding apparatus, weighted addition is performed by associating the frequency domain signals of the input channels with each other in accordance with the transform lengths thereof on the basis of transform function selection information showing the transform lengths regarding the individual frequency domain signals. This is because weighted addition (mixing) cannot be performed on the frequency domain signals of the input channels unless the windowing processes performed on the frequency domain signals of the individual input channels are the same.